With the transformation of the society and the modernization of industry and agriculture, a lot of environmental problems arise, such as the high occurrence of water pollution. The water pollution generally refers to water quality deterioration caused by the emission of a large number of toxic and harmful pollutants. It should be noted that the water pollution will greatly threaten the health and life safety of human beings and restrict the sustainable development of ecology and economy. Hence, it is of great significance to realize on-line monitoring and evaluation of water pollution.
Water pollution, caused by environmental pollutants such as organic compounds and heavy metals, has received great concern in society. The accumulation of environmental pollutants will lead to a teratogenic or carcinogenic effect in different organisms, which seriously influence the physiological mechanisms and functions of organisms, moreover, high concentration of pollutants may cause acute death to fish, invertebrates and algae. It has been found in some developing regions that the copper, lead and mercury concentrations in surface water reach 73 mg/L, 35 mg/L, and 1.14 ug/L, respectively, and other heavy metal pollutants such as manganese and chromium also seriously exceed the given standard. Therefore, the water environment safety and environment pollution control are generally concerned by society, and it is very important to achieve the monitoring of water quality.
At present, the methods for monitoring and analyzing water pollution mainly include test paper method, portable-instrument analysis and laboratory system analysis. The test paper method has large errors and is susceptible to the subjective judgment of the tester and changes of environmental parameters. The portable gas chromatography-mass spectrometry (GC-MS) can qualitatively detect the organic pollutants in the environment by combining the high resolution of gas chromatography with the strong qualification of mass spectrometer for molecules with different structures. For the voltammetry, a special electrode is necessary and the electrode needs to be frequently replaced in the actual measurement of heavy metal. In addition, the test results are susceptible to the base effect of a sample. Though the portable instrument shows strong specificity, it also has high cost. The laboratory system analysis can achieve comprehensive analysis of water pollutants, however, it fails to enable the real-time assessment of the water quality because it takes a long time in the process of water sampling-pretreatment-quality analysis, having difficulty in meeting the requirements of on-line monitoring for water pollution.
Thus, there is an urgent need to develop a method capable of on-line monitoring and evaluating the water pollution to timely and quickly assess water pollution and minimize the losses caused by sudden water pollution for economy, society and natural environment. In response to the needs of monitoring water pollution, more and more online bio-monitoring techniques have been developed and applied, including the methods based on biological indexes such as behavior and metabolism of aquatic organisms and fish electrocardio and electro-encephalo. However, the on-line monitoring techniques using behavior and metabolism as monitoring indexes have difficulties in determining the types of water pollutants. By contrast, fish electro-cardio analysis has been reported to have the potential to distinguish between organic pollutants and heavy metal pollutants. In the existing fish electro-cardio signal acquisition technology, the fish is required to be anesthetized and kept flat on a supporter for electro-cardio signal analysis, avoiding the collection of movement signals and the analysis errors. The existing methods, in which the fish is fixed by anesthesia for electro-cardio signal acquisition, have the following shortcomings.
First, the electrode is required to be connected with the electro-cardio acquisition and analysis instrument in the current methods for collecting fish electro-cardio signals to ensure the normal record, output and manual storage of the acquired electro-cardio signals, which limits the normal activities of fish in space. Specifically, the wires are limited in length and the circuit fails to be applied under water, and the smooth body surface make the fish not easy to fix, so that the acquisition instrument cannot be used on the fish or in the water just like the way that a portable electro-cardio measurer is used on human body, to collect the electro-cardio signals, failing to avoid the spatial limitation. Second, the pre-experimental anesthesia may affect the physiological and pathological characteristics of fish to a certain extent, such as heart rate, so the electro-cardio signals collected from fish under anesthesia fail to accurately reflect the normal physiological characteristics. In addition, the experimental fish is prone to death due to the lack of water and the fish cannot be maintained in a normal condition when placed flat on a laboratory bench, failing to accurately measure the electro-cardio signals.
Third, the existing methods cannot enable the long-term, real-time, on-line and continuous collection of fish electro-cardio since the fish out of water can only live for a short period, failing to accurately record and analyze the change of the electro-cardio signals over time. Therefore, in the case that the water quality changes are analyzed based on the fish electro-cardio, various electro-cardio parameters, such as changes in waveform, gap, heart rate, and heart rhythm, are required to be online collected and analyzed on the basis of the on-line collection of the fish electro-cardio signal base, so that the water quality can be online reflected by the specific changes of respective electro-cardio parameters. However, the existing electro-cardio acquisition techniques involving the use of anesthesia cannot online compare and analyze the water quality changes, so that they are rarely used in the water environment monitoring.